Crude oil is a fossil-based resource used for the production of transportation fuels, heat and power, asphalt, chemicals, adhesives, pharmaceuticals, polymers, fibers and other products. The United States is a major importer of crude oil and thus is heavily reliant on foreign countries to meet demand. Dependence on foreign oil has massive implications on national security.
National concerns over greenhouse gas emissions, carbon footprint, sustainability and the environment have grown parallel to our need for energy independence. Consequently, interest in renewable energy technologies that reduce dependence on foreign oil and lower carbon footprint has amplified, playing a noteworthy role in federal energy policy. Nonetheless, renewable energy can only supply a small fraction of total US energy consumption obligating continued crude oil imports.
Canada is the single largest exporter of crude oil into the United States making up nearly one quarter of annual crude oil imports in 2010. Over 95% of Canadian crude oil reserves are located in the province of Alberta in the form of oil sands deposits.
Oil sands are a mixture of sand, clay, water and bitumen found naturally all over the world. Bitumen, a viscous, heavy crude oil that will not flow unless heated or blended with diluent, represents about 12% of the oil sands mixture. Alberta is second only to Saudi Arabia in proven oil reserves retaining about 13% of total global reserves as of 2011 (Oil Sands Discovery Centre).
Oil sands cannot be pumped or extracted using traditional oil production methods. Instead, mining and in situ extraction methods are used to recover bitumen. Twenty percent of Canadian oil sands reserves are minable since they are within 75 meters of the surface while the remaining 80% must be recovered using in situ techniques.
One of the criticisms of oil sands production is that mining and in situ extraction techniques use more energy than traditional crude oil production. Largely because of this oil sands derived bitumen has between 5 and 15% higher greenhouse gas (GHG) emissions than average crude consumed in the US during the year 2005 (Hobbs, Brukhard, Gross, Forrest, & Groode, 2010).
A challenge for oil sands processing is that mining and in situ extraction use large amounts of water. Mining uses between three and four barrels of water per barrel of bitumen. Hot water is needed to transport oil sands and separate bitumen from clay and sand. In situ processing uses about one barrel of water per barrel of bitumen and requires substantial amounts of energy to create steam for melting bitumen underground.
Another challenge is that mining extraction requires large tailing ponds that take decades to reclaim as natural habitat and useable 1 and. Tailing ponds retain residual bitumen, water, sand and clay after separation from bitumen. Tailing ponds are made up of three primary layers: heavy sand on the bottom, relatively clean water on top and fine solids suspended in water (mature fine tailings) in the middle layer. It takes many years for fine solids to settle out and for the surface to become dry and stable enough to support equipment before tailing pond reclamation can begin (Shell Canada Limited, 2009).
Another challenge is the use of hydrocarbon diluents in bitumen transportation and chemicals to aid in bitumen separation. Mining and in situ extraction use hydrocarbon diluent to reduce bitumen viscosity and meet pipeline specifications for pipeline transport. Pipeline specifications for functional performance require a maximum crude density of 940 kg/m3 measured at 15° C. and a maximum crude viscosity of 940 cSt measured at a particular reference temperature depending on the season. Hydrocarbon diluent is composed of hydrocarbon compounds including butanes, pentanes, hexanes, heptanes, octanes, nonanes, and aromatic and cyclic hydrocarbons including benzene, toluene and xylene (Advantage Insight Group, 2007). Environmental and health concerns are associated with these products which increase the carbon footprint of the oil sand extraction process. Up to 30% vol. diluent may be added to a barrel of bitumen to meet pipeline specifications. Since diluent is not readily available near oil sands production sites it must be purchased and shipped in using pipelines or rail which adds cost and infrastructure. Furthermore, if bitumen is shipped overseas it may not be economical to ship diluent back.
Mining extraction uses additional chemicals to facilitate separation of bitumen from water, sand and clay. Typically a base (NaOH) is added with the water to produce (saponify) natural surfactants from the bitumen. This improves the separation of bitumen from oil sands minerals even though 90% of the base reacts to form bicarbonate (Schramm, Stasiuk, Yarranton, Maini, & Shelfantook, 2001).
Another challenge for oil sands bitumen is to reduce its GHG emission profile such that it meets the California Low Carbon Fuel Standard specifications and is accepted into California (Cackette, 2011).
Another challenge is using renewable energy, specifically conventional fast pyrolysis products to reduce GHG emission profile in the oil sands extraction process. Conventional bio-oil has high water content between 15-30% and high oxygen content between 35-50% making it immiscible with hydrocarbons. Conventional bio-oil also has acidic properties which limit its integration with existing equipment and processes. For example, US Patent Application Pub. No. 2011/0232164 A1 describes a process whereby biomass pyrolysis oil is used as a co-feed for a heavy petroleum oil coking process to improve operation by reducing coke drying time and improve coke handling. It is noted however that pyrolysis oil contains high oxygen which precludes it from being a direct hydrocarbon substitute though it may be soluble in high asphaltene-containing feedstocks used in coking.
Another challenge is to cost effectively separate conventional bio-oil into its aqueous (water-rich) and organic phases so that it is more easily used in oil sands processing.
What is needed in the art are methods to reduce greenhouse gas emissions, amount of process water required, length of time for tailing pond reclamation and the amount of petroleum based diluent and chemicals needed in oil sands extraction and processing. A preferred fast pyrolysis process that converts biomass into renewable bio-oil fractions and carbon-rich biochar will improve the environmental sustainability of oil sand extraction and processing when integrated with existing infrastructure.